agrep

Description

This library implements the Wu-Manber algorithm for string searching with errors, popularized by the agrep Unix command and the glimpse file indexing tool. It was developed as part of a search engine for a largish MP3 collection; the "with error" searching comes handy for those who can't spell Liszt or Shostakovitch.

Given a search pattern and a string, this algorithm determines whether the string contains a substring that matches the pattern up to a parameterizable number N of errors. An error is either a substitution (replace a character of the string with another character), a deletion (remove a character) or an insertion (add a character to the string). In more scientific terms, the number of errors is the Levenshtein edit distance between the pattern and the matched substring.

The search patterns are roughly those of the Unix shell, including one-character wildcard (?), character classes ([0-9]) and multi-character wildcard (*). In addition, conjunction (&) and alternative (|) are supported. General regular expressions are not supported, however.

The algorithm is described in S. Wu and U. Manber, Fast Text Searching With Errors, tech. rep. TR 91-11, University of Arizona, 1991.

Author

Library Procedures

Compiles a search pattern. The syntax for patterns is similar to that of the Unix shell. The following constructs are recognized:

?

match any single character

*

match any sequence of characters

[..]

character set: ranges are denoted with -, as in [a-z]; an initial ^, as in [^0-9], complements the set

&

conjunction (e.g. sweet&sour)

|

alternative (e.g. high|low)

(..)

grouping

\

escape special characters; the special characters are \?*[]&|().

The optional argument TRANSL is a character translation table.

[procedure](string->pattern STRING [TRANSL]) => PATTERN

Returns a pattern that matches exactly the given string and nothing else.

[procedure](string-match PAT STRING [NUMERRS] [WHOLEWORD]) => BOOL

Tests whether the string STRING matches the compiled pattern PAT. The optional parameter NUMERRS is the number of errors permitted. One error corresponds to a substitution, an insertion or a deletion of a character. NUMERRS default to 0 (exact match). The optional parameter WHOLEWORD is true if the pattern must match a whole word, false if it can match inside a word. It defaults to false (match inside words).

Same as substring-match, but returns the smallest number of errors such that the substring matches the pattern. That is, it returns 0 if the substring matches exactly, 1 if the substring matches with one error, etc. Returns -1 if the substring does not match the pattern with at most NUMERRS errors.

Requires

Version History

1.2 Bug fixes in pattern (thanks to felix)

1.1 Added definition of type ulong in skeleton.h

1.0 Initial Release

License

agrep was originally written by Xavier Leroy and ported to Chicken by Ivan Raikov.

Copyright 2009-2011 Ivan Raikov and the Okinawa Institute of Science
and Technology.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
A full copy of the GPL license can be found at
<http://www.gnu.org/licenses/>.